The present invention relates to a turbocompound unit, as well as to a method for manufacturing a turbocompound unit.
A turbocompound unit is a vehicle component used for recovering a pan of the energy of the exhaust gas flow and to convert that energy into a rotational movement of a shaft. The rotational movement of the shaft is transferred as a torque increase to the crankshaft of the vehicle.
Normally, the turbocompound unit has a shaft, wherein a turbine wheel is arranged at one distal end. When the internal combustion engine is running, exhaust gas will flow into the turbocompound unit and cause the turbine wheel to rotate. Hence, the shaft of the turbocompound unit will rotate accordingly.
The opposite end of the shaft is provided with a gear wheel which meshes with additional gears for causing a rotational coupling between the shaft and the crankshaft of the vehicle. When the shaft is rotating due to exhaust gas flowing through the turbocompound unit, the rotational energy of the shaft will be transferred to the crankshaft as a torque increase.
The use of turbocompound units in a vehicle has proven to provide significant advantages on driving economics as well as on the environment; the energy recovery from the exhaust gas flow will in fact reduce the fuel consumption of the vehicle.
The shaft of the turbocompound unit is allowed to rotate relative a housing, whereby it is required to support the shaft for allowing such rotation. For this, bearings are normally used.
One example of a turbocompound unit is described in WO8600665. Here, the shaft is supported by two spaced apart roller bearings arranged between the turbine wheel and the gear wheel. However, a solution of this type provides a number of drawbacks. For example, each roller bearing needs to be accurately aligned such that there are no vibrations in the shaft. Should there be only a slight difference between the alignment of the two roller bearings the efficiency of the turbocompound unit will decrease rapidly. In order to ensure proper operation of the turbocompound unit, a critical and complex assembly method is needed. Further, the bearings need to have an axial pretension. The different materials of the bearing, raceways, and the surrounding housing will cause different expansion upon temperature variations, which thus requires the pretension to be sufficiently large. Since an increased pretension is required, the bearings will consequently suffer from an increased friction.
There is thus a need for an improved turbocompound unit.
It is desirable to provide a turbocompound unit allowing for a more simple and cost-effective manufacturing.
According to a first aspect, a turbocompound unit comprises a turbine shaft, a turbine wheel supported at one end of the turbine shaft and a gear wheel supported at an opposite end of the turbine shaft. Further, the turbocompound unit comprises a rolling bearing cartridge comprising at least two axially spaced-apart raceways, each housing a plurality of rolling elements, wherein the rolling hearing cartridge is arranged concentrically on the turbine shaft between the turbine wheel and the gear wheel for allowing said turbine shaft to rotate.
The rolling elements may be balls or rollers, whereby the cartridge may be manufactured for standard rolling elements.
The turbocompound unit may further comprise a housing, wherein the rolling bearing cartridge comprises an inner race being arranged against the turbine shaft and an outer race being arranged against the housing, wherein the inner race and the outer race forms at least two axially spaced-apart raceways for rolling elements. By arranging the outer race against the housing it is possible to provide oil squeeze films between the housing and the outer race, thus eliminating the need for separate sleeves.
One lateral end of said inner race may be in contact with said gear wheel, which is advantageous in that such contact will increase the torque transfer to the gear wheel, since the axial connection between the cartridge and the gear wheel will reduce vibrations.
One lateral end of the inner race may extend into an oil slinger.
Optionally, the oil slinger may be formed integrally with the inner race. Hence, the shaft assembly is simplified since a separate step of mounting the oil slinger ring is omitted.
The oil slinger may be arranged at the lateral end of the inner race facing the turbine wheel. The oil slinger comprises a part projecting radially outwards from the lateral end of the inner race. By having an oil slinger in connection with the cartridge, the diameter of the oil slinger may be made larger and hence more effective.
The outer race may comprise at least one oil inlet arranged axially between said raceways. The outer race may further comprise at least on oil outlet arranged axially between said raceways. Hence, efficient lubrication of the bearing may be provided in a simple and reliable manner.
The oil inlet and the oil outlet may be spaced apart along the periphery of said outer race. This is advantageous in that the oil may be injected from an upper side of the cartridge, while oil may exit the cartridge at a lower side due to gravity.
According to a second aspect, an internal combustion engine is provided. The internal combustion engine comprises a turbocompound unit as described above, wherein the gear wheel is arranged to transfer torque from the turbine shaft to a crankshaft.
According to a further aspect a method for manufacturing a turbocompound unit is provided. The method comprises the steps of rotationally rigidly arranging a concentric turbine wheel on a turbine shaft at one end of the turbine shaft, inserting the turbine wheel and the turbine shaft in a housing, arranging a rolling bearing cartridge comprising at least two axially spaced-apart raceways, each housing a plurality of rolling elements, concentrically around the turbine shaft for allowing said turbine shaft to rotate relative said housing, and arranging a concentric gear wheel at an opposite end of the turbine shaft in relation to the turbine wheel.
The step of arranging a concentric gear wheel at an opposite end of the turbine shaft in relation to the turbine wheel may comprise arranging said gear wheel in close contact with said rolling bearing cartridge.